In offset printing, an image which is to be reproduced is formed on a printing plate which is attached to the surface of a plate cylinder. The image is not printed directly from the plate onto the paper, but is first transferred to an intermediate ink transfer blanket, which is mounted on a blanket cylinder. The blanket transfers (offsets) the image to a sheet of paper which is fed through the nip between an impression cylinder and the blanket cylinder. The offset printing press thus includes three rotatable cylinders, the plate cylinder which carries the printing plate, the blanket cylinder which has an ink receptive surface for receiving the inked image, and the impression cylinder which presses the paper against the blanket so that the inked image is transferred to the paper.
The blanket has an ink transfer surface made of an ink receptive (oleophilic) material. Paper fed between the blanket cylinder and the impression cylinder receives the inked image directly from the blanket to complete the offset printing process. The position of the impression cylinder relative to the blanket cylinder is adjustable so that the printing pressure applied to the sheet may be adjusted to obtain a clean transfer of ink, without crushing or otherwise deforming the blanket.